Salts of polyoxyalkylene alkyl ether carboxylic acid are compounds produced by substituting polyoxyalkylene alkyl ether with carboxylic acid at the terminal end of the ether, and are known as a useful surfactant used in cosmetics, emulsifiers, solubilizers, dispersants, gelling agents, and detergent bases, and the like. The salts can be modified in properties by changing pH. These salts have good stability against hard water. Aqueous solutions thereof are stable to various polyvalent metal ions such as an aluminum ion, gentle to the skin, and have small inhibitory effects on enzymes. The salts are thus expected to have various applications.
There have been various known methods for producing a salt of polyoxyalkylene alkyl ether carboxylic acid. One of the methods in which polyoxyalkylene alkyl ether is oxidized with oxygen in the presence of a noble metal catalyst is known (JP-A 56-169644, JP-A 62-198641, and JP-A 62-269746). JP-A 01-146840 describes addition of an ether carboxylic acid to a polyalkoxy alcohol or a fatty alcohol alkoxylate in oxidation of the polyalkoxy alcohol or the fatty alcohol alkoxylate to produce the ether carboxylic acid.